Product category:
Gauges, Indicators and Instruments
News Release from: Magna Projects and Instruments | Subject: Tattersall Two-Point Workability Test
Edited by the Engineeringtalk Editorial
Team on 11 January 2002
Getting solid data on the consistency of
cement
Magna Projects and Instruments has been licensed to develop and market a rugged machine for the Tattersall Two-Point Workability Test for fresh cement and concrete
Magna Projects and Instruments has been licensed by Heriot-Watt University and the University College of London (UCL) to develop and market the Tattersall Two-Point Workability Test (TTPT) for fresh cement and concrete This instrument, which was developed over the past 25 years of so at Sheffield University by Dr Geoff Tattersall, is designed to provided some solid engineering data on the consistency of mixes such as cement and concrete pastes
This article was originally published on Engineeringtalk on 8 Mar 2001 at 8.00am (UK)
Related stories
Processability data at real processing rates
Magna's capillary extrusion rheometers generate processability data at real processing rates.
Magna to supply NPL viscosity apparatus
Magna Projects and Instruments Limited has been awarded an exclusive licence by the UK's National Physical Laboratory to manufacture and market NPL's PCV Pressure Coefficient of Viscosity apparatus
Such data is vital for batch-to-batch quality control, and to ensure, for example, that unsuitable batches of material are not inadvertently poured onto such structures reinforced concrete buildings, thereby creating potential weak spots.
Cement and concrete pastes flow in a distinct way, behaving as "Bingham Fluids".
That is to say, they do not start to flow until a characteristic "Yield Stress" had been exceeded (a useful feature, as this allows the mix to stay in position until it sets), and then they flow in a linear or Newtonian manner, ie the shear stress (force) increases proportionally to the shear rate (speed).
Further reading
NPL award licence to manufacture rheology analyser
Magna Projects and Instruments have been awarded the licence by NPL to manufacture and market the IMAS in-line/on-line rheology analyser for injection moulding machines.
Testing the flow properties of fresh cement
Magna Projects and Instruments has licensed from University College London and Herriot-Watt Universities a rugged instrument for testing the flow properties or rheology of fresh cement and concrete
Thus, the material may be characterised by the Yield Stress and by the slope of the ensuing straight line, which is, in fact, the plastic viscosity.
The TTPT is a rugged machine which may be used in the research and development or QA/QC laboratory or on site.
The principle of operation is to rotate a paddle in the sample - typically 20 - 30 litres - and to measure the torque required to rotate the paddle over range of speeds.
The torque vs speed curve then enables the Two Points to be evaluated.
The instrument may be operated in relative mode, or may be calibrated using materials of known rheology.
Two paddle geometries are available - a helical paddle, which rotates centrally, or an H-bladed paddle which rotates on a planetary gear for materials to avoid cavitation in susceptible formulations.
The instrument is fully guarded, and is automated so that it may be operated in constant speed, staircase or ramp speed modes.
Torque is measured by monitoring the oil pressure in the drive chain, and this is displayed on a panel-mounted pressure gauge and recorded by a computer via a pressure transducer.
Similarly, speed may be monitored and controlled by the computer, or may be changed manually.
Shear pins protect the drive against inadvertent overloads due, for example, to clumps of aggregate.
The TTPT may be hosed clean if required.
• Magna Projects and Instruments: contact details and other news
• Email this article to a colleague
• Register for the free Engineeringtalk email newsletter
• Engineeringtalk Home Page
Search the Pro-Talk network of sites
